380 The Iowa and Illinois Tornado. (July, 
centripetal current was not greatly exceeded by that of the 
centrifugal. 
The Dimensions of the Funnel.—The data for calculating 
the dimensions of the visible portion of the funnel are 
more numerous than precisely accurate; but I conclude that 
the tornado column was, from a favourable position, visible at 
some parts of its course to a height of between r and 
2 miles. 
Wherever there was evidence of the funnel having 
touched the ground there was, to a greater or less breadth, 
what I have designated as the vortex of extreme violence, 
varying from roo yards in breadth to nothing. Without 
having positive evidence, and notwithstanding that there 
was everywhere a gradual diminution of violence from the 
centre to the circumference except in the remarkable 
phenomenon of streaks or arms, and no abrupt transitions, 
I could not help concluding that the path of greatest violence 
was identical, or nearly so, with the diameter of the base of 
the funnel when it touched the ground. This would give it 
an average diameter of about 30 yards. The witnesses are 
generally agreed that the summit was several times wider 
than the base. If we assume that the visible top was five 
times the diameter of the base, we have, say, for the altitude 
of 1 mile, a diameter of only 150 yards. I think, however, 
that, owing to its great elevation and the optical delusion 
connected therewith, and the general belief of the spectators, 
that the funnel was, at the very utmost, only a few hundred 
feet high; the diameter of the summit was very much greater. 
The Changes scen in the Funnel.—Some observers saw only 
one funnel, others saw two funnels superimposed with the 
narrow ends together, and the smaller one beneath, while a 
great many saw two and even three funnels side by side. 
The evidence on all these points is beyond question. At 
first I was inclined to believe that two or more funnels had 
actually touched the ground and travelled side by side. The 
sketch of the storm by R. F. Campbell seemed to favour 
this explanation. It shows a protuberance on each side of 
the funnel, which looks like an inceptive funnel. The fact 
that a second funnel should travel along the south-east side 
of the main one without disturbing the symmetry of the 
action of the latter, as exhibited by the ruins, did not appear 
altogether incredible, for it is abundantly evident from the 
statement of facts that the damage was done by a wind 
blowing in the path of the tornado when the black funnel 
hovered above or slightly touched the ground. Thus an 
incipient funnel, moving along the south-east side of the 
